Eli5 Why do they say take 3 or 4 deep breaths before a deep dive?
In: Biology
When you exhale, you don’t actually get _all_ of the air out of your lungs. There is still some ‘stale air’ in there that hasn’t been circulated (known as the residual volume – give or take about 1/2-1/3 of the total lung volume). By taking a few deep breaths in rapid succession, you cycle out as much of that stale air as possible, giving you as much fresh air in the lungs as possible.
It’s a combination of purging CO2 from your lungs and oxygenating your blood. As a teen I used to hyperventilate at the poolside until dizzy and then bash out underwater lengths. Notably increases the duration you can stay under, I was never able to cover 50m without this
It helps to saturate the lungs with more fresh air. You exchange air decently with normal breathing, but a few nice deep breaths can expel a little extra old stuff and get in a little extra fresh.
From what I think I know, lack of oxygen isn’t what makes you want to breathe when underwater, It’s the buildup of carbon dioxide. By taking a few deep breaths, you get as much carbon dioxide out as possible, to extend the buildup time when underwater
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